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Tom, Liya (2024) Design, development and manufacturability study of aerospace actuator motor. PhD thesis, University of Nottingham.

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Abstract

Climate change concerns and its impact on the environment have prompted the aviation industry to explore more electric and hybrid aircraft solutions, given that the aerospace sector contributes approximately 2% of global CO2 emissions. After conducting a comprehensive study of the three primary areas of electrification which includes, propulsion, power generation, and actuation, it was determined that this thesis would primarily focus on actuation due to the allocated timeframe and cost constraints.

As electric motors are a crucial component in more electric aircraft systems, careful design and selection is a critical aspect. When designing an electric motor tailored for aerospace applications, key factors such as weight, volume, reliability, efficiency, and cost must be considered. In line with these stringent constraints, this thesis introduces various innovative ideas aimed at reducing the weight and size of the electric motor whilst ensuring reliability and fault tolerance. Additionally, the research explores methods to simplify the manufacturing process, to advance the development of more efficient aircraft systems.

The initial phase of the thesis concentrates on understanding the design requirements essential to meet the stringent targets set by the aerospace industry. Permanent Magnet machines with a Halbach array rotor are preferred for actuation applications, due to their advantageous characteristics such as, high efficiency, power density, power factor and fault tolerance. Subsequently, a benchmark model was designed and optimised both electrically and thermally. Following the successful design, the benchmark model was fabricated and subjected to comprehensive testing, ensuring all design requirements are met and that it demonstrates reliability even under fault conditions such as open and short circuits.

The first novel approach in this study addresses manufacturing imperfections in Halbach array rotors. Traditional fabrication of Halbach array rotors with rare earth permanent magnets involves a labour-intensive, time-consuming process with specialist tools and higher expenses, whilst ensuring proper orientation and placement within tolerance. Despite the benefits, there is limited research on manufacturing aspects related to Halbach array rotors. Hence, a new manufacturing method is proposed in this thesis to simplify the conventional approach, reducing costs, time, and complexity. The novel methodology presented involves a magnet retention ring with empty slots, allowing magnets to be easily slid into place, ensuring correct orientation and placement. This approach offers a reliable, repeatable, and efficient manufacturing process, which can be carried out in a very short period of time, and it is demonstrated successfully on motorettes.

The next innovative approach in this study aims to lightweight the shaft, by exploring carbon fibre reinforced plastic. While literature suggests high potential for weight reduction using composite material, its validation in electric motors remains largely unexplored. This study introduces two methods employing carbon fibre shafts: a) a hybrid shaft combining carbon fibre and stainless steel, and b) a solitary carbon fibre shaft, which only has carbon fibre in the active part of the machine. These models are designed and analysed against the conventional solid steel shaft. Due to time constraints, only the solitary carbon fibre shaft was fabricated. When comparing the fabricated solitary carbon fibre shaft against the steel shaft, approximately 46% reduction in shaft weight was noted, making this innovation suitable for various industries, particularly aerospace.

Once both of these innovative ideas were fabricated and implemented on to the rotor, a comprehensive testing was carried out. This testing encompassed electrical, thermal, and vibrational tests, as well as fault condition testing such as open and short circuits. The experimental results were then compared against finite element analysis results to verify the accuracy. It was found that the results closely matched the simulations, confirming that the machine operates successfully as expected. Moreover, the machine exhibited robustness, staying comfortably within the temperature range even when subjected to fault conditions, for the specified duty cycle. The assembly and innovative ideas implemented remained intact and successfully survived all the testing, affirming that the enhancements in manufacturing efficiency for Halbach rotors, as well as advancements in lightweighting and power density, can indeed be achieved with the novelties outlined in the thesis.

The final part of the thesis focused on investigating slot shapes and associated winding configurations to enhance motor efficiency and performance. When analysing the literature, it was found that various winding technologies have the potential to enhance the slot fill factor and consequently improve the efficiency and performance of the motor. However, for practical implementation of these technologies, specific stator configurations that supports their integration is required. Two stator configurations are explored in this part of the thesis, which includes open parallel slot and modular closed slot stator. Several designs iterations and optimisations of open and closed slot stators were conducted and compared against the conventional semi-open benchmark model. Once optimised, the best model in terms of active mass was selected for both stator configurations. Due to time constraints, experiments initially prioritised the open parallel slot stator, which allows implementation of innovative winding solutions like rectangular wires. Once the open slot stator was fabricated two winding technologies were selected for further exploration namely, compressed windings and custom foil windings.

During the manufacturing process, it was discovered that the designated number of turns, as per the design was not feasible with the foil windings. Consequently, for consistency, the same number of turns as the foil windings were implemented on the compressed windings, resulting in approximately 20% reduction in turns. As the focus of the study was on improving manufacturing, it was observed that these winding technologies have made manufacturing more challenging to implement. Unfortunately, an unexpected wire breakage also occurred with the preformed compressed winding during the rotor assembly. These difficulties, compounded by the small stator size, led to the decision to halt further study on slot shape and winding configurations, as reproducing or altering the stator may not ensure anticipated improvements in the given timeframe of the project.

Overall, the innovative ideas have demonstrated methods to enhance manufacturing efficiency and create a light weight, power-dense motor. Despite the unexpected challenges encountered in the final study, valuable insights were gained into slot shape and winding technologies. These findings can serve as a foundation for future research aimed at improving slot fill factor and motor efficiency.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Vakil, Gaurang Khowja, Muhammad Gerada, Chris Cairns, Alasdair
Keywords:	Actuation; Electric motors; Aircraft motors; Efficient aircraft systems; Halbach array rotors; Carbon fibre shafts; Slot stators; Winding technologies
Subjects:	T Technology > TL Motor vehicles. Aeronautics. Astronautics
Faculties/Schools:	UK Campuses > Faculty of Engineering > Department of Electrical and Electronic Engineering
Item ID:	78291
Depositing User:	Tom, Liya
Date Deposited:	18 Jul 2024 04:40
Last Modified:	18 Jul 2024 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/78291

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